The present invention relates to Schottky Barrier devices, and more particularly to Schottky Barrier devices which are readily integratable into integrated semiconductor circuits.
Surface barrier devices utilizing the Schottky effect based upon the rectifying characteristics exhibited by a metal-to-semiconductor interface are well known. Schottky Barrier diodes also called "hot carrier" diodes have been recognized to exhibit fast switching speeds as well as relatively low forward barrier or turn-on voltages. Accordingly, the desirability of utilizing Schottky Barrier devices in integrated monolithic circuits has been recognized in the art. The two most desirable uses of Schottky Barrier diodes have been purely as clamps or shunts across PN semiconductor junctions as well as for storage purposes in Schottky Barrier diode monolithic memory array integrated circuits. The primary advantage of Schottky Barrier diodes over other diodes has been their relatively low forward barrier characteristics. Because of such low forward barrier characteristics, Schottky Barrier diode clamps may be used to prevent transistor saturation and thereby to provide faster turn-off time for digital circuitry, and faster switching speeds. Also, such diodes require less voltage when used in memory arrays, thereby having minimal heat and power dissipation problems.
One extensively used metallurgy for providing the ohmic contacts and interconnections in present integrated circuitry involves the use of a layer of platinum silicide in the contact holes making direct contact with the silicon substrate and a layer of aluminum over the platinum silicide. This layer of aluminum is coextensive with an aluminum layer pattern on the insulative layer over the semiconductor substrate which provides the interconnections. The reason that platinum silicide has been used in the contact holes is that aluminum has been found to make less than satisfactory direct ohmic contacts with silicon semiconductor substrates.
While such composite metallurgies of aluminum layers over platinum silicide have been extensively used in integrated circuits involving ohmic contacts and even suggested for usage in circuitry involving both ohmic and Schottky Barrier contacts (see U.S. Pat. No. 3,506,893), problems have been encountered in the fabrication.
Generally, in the process of forming the platinum silicide contacts, a relatively thin layer of a patterned dielectric or insulating film on a silicon semiconductor substrate is provided with contact openings in those areas where a Schottky Barrier diode is to be formed. A thin layer of platinum is deposited over the entire surface by any conventional deposition technique, such as vapor deposition or preferably sputtering. On short term heat treatment, the platinum in the contact holes combines with the silicon to form the platinum silicide. The uncombined platinum layer is then removed so as to retain the platinum silicide in the contact holes.
Although the sputter etching of platinum has been known heretofore (see for example U.S. Pat. Nos. 3,271,286 and 3,975,252), due to the similar sputter etch rates for platinum (about 95A/min.) and platinum silicide (about 80A/min.), removal of the uncombined platinum has been conventionally effected by wet etching with etchants such as aqua regia. (See U.S. Pat. Nos. 3,271,286, 3,855,612, 3,956,527, 3,968,272 and 3,995,301).
Drawbacks of such etchants are the prospect of contamination by the various etchants, lack of any substantial differentiation in etching rates of the platinum and its silicide, as well as associated handling in rinsing and drying operations.
It has been discovered in accordance with this invention that substantially increased differentiation of the sputter etch rate of platinum can be obtained relative to the sputter etch rate of platinum silicide by effecting the sputter etching in an ambient of a rare gas containing at least 1% by volume of oxygen or nitrogen, and preferably an ambient of argon containing 10% by volume of oxygen.